Yesterday, we introduced the six major forms of energy. Today, we take a deep dive into each one. For every form, we will explore three questions: What causes it? How does it behave? Where do we see it in the real world?

## Thermal Energy: The Energy of Moving Particles

All matter is made of tiny particles (atoms and molecules) that are always in motion. Thermal energy is the total kinetic energy of all these particles. When particles move faster, the substance has more thermal energy and its temperature is higher. When particles slow down, the substance cools.

Key facts about thermal energy: - Thermal energy always flows from warmer objects to cooler objects, never the reverse - Adding thermal energy to a solid can cause it to melt (change to a liquid); adding more can cause it to boil (change to a gas) - Removing thermal energy causes the reverse: gas condenses to liquid, liquid freezes to solid - Rubbing your hands together generates thermal energy through friction

## Light Energy: Electromagnetic Waves

Light energy, also called radiant energy, is energy that travels as electromagnetic waves. These waves do not need a medium to travel; they can move through the vacuum of space. This is how sunlight reaches Earth across 150 million kilometers of empty space.

Visible light is only a small part of the electromagnetic spectrum, which also includes radio waves, microwaves, infrared, ultraviolet, X-rays, and gamma rays. All of these are forms of radiant energy, but our eyes can only detect the visible portion.

Key facts about light energy: - Light travels at approximately 300,000 kilometers per second - Light can be reflected (bounced off surfaces), refracted (bent through different materials), and absorbed (converted to thermal energy) - Plants use light energy from the sun to make food through photosynthesis

## Sound Energy: Vibrations Through Matter

Sound energy is produced when an object vibrates, creating compression waves that travel through a medium such as air, water, or a solid material. Unlike light, sound CANNOT travel through a vacuum because it needs particles to carry the vibration from one place to another.

Key facts about sound energy: - Sound travels fastest through solids, slower through liquids, and slowest through gases - Pitch (how high or low a sound is) depends on the frequency of vibration: more vibrations per second = higher pitch - Volume (how loud or soft a sound is) depends on the amplitude of the wave: bigger vibrations = louder sound - The speed of sound in air at room temperature is about 343 meters per second, much slower than light

## Electrical and Chemical Energy

Electrical energy is the energy of moving electric charges (electrons). When electrons flow through a wire, they carry energy that can power lights, motors, heaters, and screens. Lightning is a dramatic natural example of electrical energy. In our homes, electrical energy is delivered through circuits from power plants.

Chemical energy is energy stored in the bonds between atoms within molecules. When these bonds are broken through chemical reactions, the stored energy is released. Combustion (burning) is one of the most common chemical reactions that releases chemical energy. When you burn wood, the chemical bonds in the wood molecules break apart, releasing thermal energy (heat) and light energy (the flame). Your body uses a similar process: it breaks down molecules in food to release the energy your cells need.

Mechanical energy is the sum of kinetic and potential energy in a system. A pendulum swinging, a wheel turning, a ball rolling, all demonstrate mechanical energy as it shifts between kinetic and potential forms.